Imaging lens and solid state imaging device

ABSTRACT

According to one embodiment, an imaging lens includes a first optical system and a microlens array. The first optical system includes an optical axis. The microlens array is provided between the first optical system and an imaging element. The microlens array includes microlens units provided in a first plane. The imaging element includes pixel groups. Each of the pixel groups includes pixels. The microlens units respectively overlap the pixel groups when projected onto the first plane. The first optical system includes an aperture stop, and first, second, and third lenses. The first lens is provided between the aperture stop and the microlens array, and has a positive refractive power. The second lens is provided between the first lens and the microlens array, and has a negative refractive power. The third lens is provided between the second lens and the microlens array, and has a positive refractive power.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2013-193518, filed on Sep. 18, 2013; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an imaging lens and asolid state imaging device.

BACKGROUND

Various methods are being used as imaging technology that can obtainlengths in the depth direction of a subject as two-dimensionalinformation (a range image) such as technology that uses a referencebeam to measure the reflected light intensity and/or return time fromthe subject, stereoscopic ranging technology using multiple cameras,etc. Better subject recognition is possible by using range imageinformation than by using the image information obtained from a normalcamera. Therefore, the demand is increasing for applications of rangeimage information as new input information in relatively inexpensiveproducts for appliances, games, industrial applications, etc.

Among distance imaging methods, a solid state imaging device thatincludes an imaging optical system and multiple optical systems has beenproposed as a configuration in which a single camera is used to obtainmany sets of parallax and the ranging is performed based ontriangulation. In such a solid state imaging device, multiple opticalsystems are disposed as a re-imaging optical system between the imagingoptical system and the imaging element. For example, a microlens arrayin which many microlenses are formed on a plane is used as the multipleoptical systems.

Multiple pixels are disposed under each of the microlenses. The imagesthat are demagnified by the imaging optical systems are imaged on theimaging element by the microlens array. The simple-eye images that areimaged have viewpoints shifted by the amount of parallax existing due tothe arrangement position of each microlens.

The distance estimation of the subject is possible using the principleof triangulation by performing signal processing of the images of theparallax image groups obtained from many microlenses. Further, it ispossible to reconstruct the images as a two-dimensional image byperforming image processing to link the images together.

In an imaging lens and a solid state imaging device, it is desirable toacquire both a high-precision range image and a good visible image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a solid state imaging deviceaccording to the embodiment;

FIG. 2 is a schematic cross-sectional view illustrating the solid stateimaging device according to the embodiment;

FIG. 3A and FIG. 3B illustrate the relationship between groups of lightrays and the distance from the subject to the imaging lens;

FIG. 4 illustrates the geometrical optical relationship of themicrolenses at the optical-axis center of the imaging lens;

FIG. 5A to FIG. 5C illustrate the overlapping field of view relationshipof the microlenses;

FIG. 6A to FIG. 6E illustrate the method for reconstructing thetwo-dimensional image;

FIG. 7 illustrates the arithmetic average;

FIG. 8 shows the heights of light rays passing through the lens crosssections;

FIG. 9 shows the flattening of the exit pupil;

FIG. 10 illustrates the configuration of the imaging lens according tothe embodiment;

FIG. 11 is a schematic plan view illustrating the arrangement of themicrolens units;

FIG. 12 is a ray diagrams of the microlenses;

FIG. 13 is a ray diagrams of the microlenses;

FIG. 14 is a ray diagram of a microlens;

FIG. 15 shows aberration curves of the microlens;

FIG. 16 is a ray diagram of the microlens;

FIG. 17 shows aberration curves of the microlens;

FIG. 18 is a ray diagram of the microlens;

FIG. 19 shows aberration curves of the microlens;

FIG. 20 illustrates the configuration of an imaging lens according to afirst example;

FIG. 21 is various aberration diagrams of the imaging lens according tothe first example;

FIG. 22 is various aberration diagrams of the imaging lens according tothe first example;

FIG. 23 illustrates the exit pupil position of the imaging lensaccording to the first example;

FIG. 24 illustrates the configurations and numerical values of the exitpupils of the imaging lens according to the first example;

FIG. 25 illustrates the configuration of an imaging lens according to asecond example;

FIG. 26 is various aberration diagrams of the imaging lens according tothe second example;

FIG. 27 is various aberration diagrams of the imaging lens according tothe second example;

FIG. 28 illustrates the exit pupil position of the imaging lensaccording to the second example;

FIG. 29 illustrates the configurations and numerical values of the exitpupils of the imaging lens according to the second example;

FIG. 30 illustrates the configuration of an imaging lens according to athird example;

FIG. 31 is various aberration diagrams of the imaging lens according tothe third example;

FIG. 32 is various aberration diagrams of the imaging lens according tothe third example;

FIG. 33 illustrates the exit pupil position of the imaging lensaccording to the third example;

FIG. 34 illustrates the configurations and numerical values of the exitpupils of the imaging lens according to the third example;

FIG. 35 illustrates the configuration of an imaging lens according to afourth example;

FIG. 36 is various aberration diagrams of the imaging lens according tothe fourth example;

FIG. 37 is various aberration diagrams of the imaging lens according tothe fourth example;

FIG. 38 illustrates the exit pupil position of the imaging lensaccording to the fourth example; and

FIG. 39 illustrates the configurations and numerical values of the exitpupils of the imaging lens according to the fourth example.

DETAILED DESCRIPTION

According to one embodiment, an imaging lens includes a first opticalsystem and a microlens array. The first optical system includes anoptical axis. The microlens array is provided between the first opticalsystem and an imaging element. The microlens array includes a pluralityof microlens units provided in a first plane. The imaging elementincludes a plurality of pixel groups. Each of the pixel groups includesa plurality of pixels. The microlens units respectively overlap thepixel groups when projected onto the first plane. The first opticalsystem includes an aperture stop, a first lens, a second lens, and athird lens. The first lens is provided between the aperture stop and themicrolens array, and has a positive refractive power. The first lens hasa first surface, and a second surface, the first surface opposing theaperture stop, the second surface being provided between the firstsurface and the microlens array. The second lens is provided between thefirst lens and the microlens array, and has a negative refractive power.The second lens has a third surface, and a fourth surface, the thirdsurface opposing the second surface, the fourth surface being providedbetween the third surface and the microlens array. The third lens isprovided between the second lens and the microlens array, and has apositive refractive power. The third lens has a fifth surface, and asixth surface, the fifth surface opposing the fourth surface, the sixthsurface being provided between the fifth surface and the microlensarray. A curvature radius of the first surface is positive. A curvatureradius of the third surface and a curvature radius of the fourth surfaceare negative. A curvature radius of the fifth surface and a curvatureradius of the sixth surface are positive. At least one selected from thefirst to sixth surfaces has an aspherical configuration. Formulas (1) to(6) are satisfied, where f is a focal length of the first opticalsystem, f1 is a focal length of the first lens, f2 is a focal length ofthe second lens, f3 is a focal length of the third lens, TL is adistance between the aperture stop and the imaging element, D2 is adistance along the optical axis between the second lens and the thirdlens, and D5 is a thickness along the optical axis of the third lens:0.6<f1/f<0.9  (1)1.0<|f2|/f<3.0  (2)2.0<f3/f<200  (3)f/TL<1.3  (4)0<D2/f<0.2  (5)0<D5/f<0.5  (6).

Various embodiments will be described hereinafter with reference to theaccompanying drawings. In the description hereinbelow, similar membersare marked with like reference numerals, and a description is omitted asappropriate for members once described.

Configuration of Camera Module

FIG. 1 is a block diagram illustrating a solid state imaging deviceaccording to the embodiment.

The solid state imaging device 1 shown in FIG. 1 is, for example, acamera module.

As shown in FIG. 1, the solid state imaging device 1 includes an imagingmodule unit 10 and an imaging signal processor (hereinbelow, also calledan ISP (Image Signal Processor)) 20.

The imaging module unit 10 includes an imaging optical system (a firstoptical system) 12, a microlens array 14 (hereinbelow, also called theMLA (Micro Lens Array)), an imaging element (a solid-state imagingelement 16), and an imaging circuit 18.

The imaging optical system 12 functions as an imaging optical systemthat guides the light from the subject onto the solid-state imagingelement 16. The solid-state imaging element 16 functions as an elementthat converts the light guided by the imaging optical system 12 into asignal charge. Multiple pixels (e.g., photodiodes used as photoelectricconversion elements) are arranged in a two-dimensional arrayconfiguration along the light reception surface.

The microlens array 14 includes, for example, multiple microlens units14 a. The microlens units 14 a may be micro-optical systems such asprisms, etc. The individual microlens units 14 a of the microlens array14 demagnify the group of light rays that is imaged at the imaging plane(the virtual imaging plane) by the imaging optical system 12. The imagethat is demagnified by each of the microlens units 14 a is imaged on apixel block (a group of multiple pixels) corresponding to the microlensunit 14 a.

The imaging circuit 18 includes a drive circuit unit (not shown) thatdrives the pixels of the pixel array of the solid-state imaging element16, and a pixel signal processing circuit unit (not shown) thatprocesses the signals output from the pixel region.

The drive circuit unit includes, for example, a vertical selectioncircuit that sequentially selects the pixels to be driven in thevertical direction by horizontal line (row) units, a horizontalselection circuit that sequentially selects the pixels to be driven bycolumn units, and a TG (a timing generator) circuit that drives thevertical selection circuit and the horizontal selection circuit byvarious pulses.

The pixel signal processing circuit unit includes an AD conversioncircuit that performs digital conversion of the analog electricalsignals from the pixel region, a gain control/amplifier circuit thatperforms gain control and/or amplifier operations, and a digital signalprocessing circuit that performs correction processing of the digitalsignals, etc.

The ISP 20 includes a camera module I/F (an interface) 22, an imageacquisition unit 24, a signal processing unit 26, and a driver I/F 28.The image acquisition unit 24 acquires, from the camera module I/F 22,the raw image obtained by the imaging by the imaging module unit 10.

The signal processing unit 26 implements signal processing of the rawimage acquired by the image acquisition unit 24. The driver I/F (theinterface) 28 outputs the image signal that has undergone the signalprocessing of the signal processing unit 26 to a not-shown displaydriver. The display driver displays the image that is imaged by thesolid state imaging device 1.

Member Configuration of Camera Module

FIG. 2 is a schematic cross-sectional view illustrating the solid stateimaging device according to the embodiment.

In the solid state imaging device 1 according to the embodiment as shownin FIG. 2, the solid-state imaging element 16 is formed in asemiconductor substrate 16 a. The solid-state imaging element 16includes multiple pixel groups 16 e. Each of the multiple pixel groups16 e includes multiple pixels 16 b. The multiple pixels 16 b includephotodiodes and are provided on the semiconductor substrate 16 a. Thepitch (the pixel pitch) between the mutually-adjacent pixels 16 b is,for example, not less than about 0.7 micrometers (μm) and not more thanabout 2.7 μm. The size of the solid-state imaging element 16 is, forexample, not less than about 3.0 millimeters (mm) and not more thanabout 6.0 mm in the longitudinal direction and not less than about 4.0mm and not more than about 8.0 mm in the lateral direction. The volumeof the entire solid state imaging device 1 is, for example, about 1cubic centimeter (cm³).

A drive/read-out circuit (not shown) that drives the pixels 16 b andreads the signals from the pixel 16 b is formed on the semiconductorsubstrate 16 a.

On each of the multiple pixels 16 b, a color filter 16 c of R (having ahigh transmittance for light of the red wavelength light region), G(having a high transmittance for light of the green wavelength lightregion), B (having a high transmittance for light of the blue wavelengthlight region), or W (transmitting red, green, and blue wavelength light)is formed for every pixel 16 b. A pixel concentrating microlens 16 d maybe formed at the upper portion of the color filter 16 c every one pixel16 b.

The microlens array 14 is disposed on the color filter 16 c. Themicrolens array 14 includes a visible light-transmissive substrate 14 b,and the microlens units 14 a formed on the visible light-transmissivesubstrate 14 b. The microlens units 14 a are disposed on the solid-stateimaging element 16 side as viewed from the visible light-transmissivesubstrate 14 b. The multiple microlens units 14 a are provided in afirst plane 14 p. The multiple microlens units 14 a are arranged in atwo-dimensional array configuration on the visible light-transmissivesubstrate 14 b. The microlens units 14 a are provided to correspond tothe pixel blocks made of the multiple pixels 16 b provided on thesemiconductor substrate 16 a. In other words, the multiple microlensunits 14 a respectively overlap the multiple pixel groups 16 e whenprojected onto the first plane 14 p. Each of the microlens units 14 afunctions as an optical system that performs demagnification and imagingonto the corresponding pixel block.

The visible light-transmissive substrate 14 b is provided to beseparated from the solid-state imaging element 16. A spacer 42 thatincludes a resin material, etc., is provided between the visiblelight-transmissive substrate 14 b and the semiconductor substrate 16 ain which the solid-state imaging element 16 is formed. The visiblelight-transmissive substrate 14 b is bonded to the semiconductorsubstrate 16 a via the spacer 42. The alignment when bonding thesemiconductor substrate 16 a and the visible light-transmissivesubstrate 14 b is performed using an alignment mark, etc., as areference.

The visible light-transmissive substrate 14 b may be a material that notonly transmits visible light but also cuts, for example, unnecessarynear-infrared light. A multilayered film or a single-layer film thattransmits visible light and reflects near-infrared light may be formedin the visible light-transmissive substrate 14 b.

Also, an optical filter 43 is provided at the upper portion of thevisible light-transmissive substrate 14 b as necessary. In the example,the optical filter 43 is provided between the imaging optical system 12and the microlens array 14. In the case where the visiblelight-transmissive substrate 14 b does not function to cut near-infraredlight, the optical filter 43 that has a similar function is disposedseparately.

Further, an electrode pad 44 for reading the pixels 16 b is provided inthe semiconductor substrate 16 a. A vertical electrical connection 46that is electrically connected to a processing and driver chip is madein the lower portion of the electrode pad 44 to pierce the semiconductorsubstrate 16 a.

The semiconductor substrate 16 a is electrically connected to theprocessing and driver chip 50 via the vertical electrical connection 46and a bump 48. The drive processing circuit (the imaging circuit 18)that drives the solid-state imaging element 16 and processes the signalsthat are read is formed in the processing and driver chip 50. Theelectrical connection between the semiconductor substrate 16 a and theprocessing and driver chip 50 is not limited to the vertical electricalconnection 46; and the electrical connection may be made by a metalwire, etc., between electrode pads provided on the two chips.

The imaging optical system 12 is provided above the visiblelight-transmissive substrate 14 b. The imaging optical system 12includes multiple lenses. The imaging optical system 12 is mounted to alens optical column 62. The lens optical column 62 is mounted to a lensholder 64. Due to the relationship between the insertion pressure andthe output image, the mounting position of the imaging optical system 12may be adjusted when mounting the lens holder 64.

A light-shielding cover 52 that shields unnecessary light is mountedaround the semiconductor substrate 16 a, the visible light-transmissivesubstrate 14 b, and the processing and driver chip 50. A moduleelectrode 54 that electrically connects the processing and driver chip50 to the outside is provided in the lower portion of the processing anddriver chip 50.

Microlens Geometrical Optical Relationship Diagram

The geometrical optical relationship of the optical system (the virtualimage optical system) of the solid state imaging device 1 of theembodiment will now be described.

FIG. 3A and FIG. 3B illustrate the relationship between groups of lightrays and the distance from the subject to the imaging lens.

FIG. 4 illustrates the geometrical optical relationship of themicrolenses at the optical-axis center of the imaging lens.

FIG. 5A to FIG. 5C illustrate the overlapping field of view relationshipof the microlenses.

The imaging optical system 12 has an optical axis Ox. In the descriptionhereinbelow, only the area proximal to the optical axis of the lenses ofthe imaging optical system 12 is described for simplification.

When considering only the imaging optical system 12, a chief ray from asubject point P on the optical axis and peripheral rays which are fromthe same family of light rays as the chief ray are imaged at a virtualimaging plane 70 which is determined by the focal length f of theimaging optical system and a distance A between the imaging opticalsystem 12 and the subject point 100P so that the relationship of Formula1 is satisfied.

$\begin{matrix}{\frac{1}{f} = {\frac{1}{A} + \frac{1}{B}}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, f is the focal length of the imaging optical system 12, A is thedistance from an object-side principal plane 12 a of the imaging opticalsystem 12 to the subject point 100P, and B is the distance from animage-side principal plane 12 a of the imaging optical system 12 to avirtual imaging point P′70. The image magnification (the horizontalmagnification) of the imaging optical system 12 expressed by Formula 2recited below.

$\begin{matrix}{M = \frac{B}{A}} & \left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Here, in the embodiment, the virtual imaging point P′70 of the imagingoptical system 12 is positioned rearward (on the side opposite to thesubject 100) of the solid-state imaging element 16. In other words, thesolid-state imaging element 16 is provided between the virtual imagingpoint P′70 and the imaging optical system 12. For example, the virtualimaging point P′70 is a point that is positioned at the focal length ffrom the imaging optical system 12. In such a case, because themicrolens units 14 a are disposed frontward of the virtual imaging pointP′70, the light is concentrated onto the surface of the solid-stateimaging element 16 that includes the pixels and is positioned frontwardof the virtual imaging plane 70. In such a case, groups of light rays 80and 82 are demagnified and imaged with a virtual image relationship. Theoptical imaging system of the microlens units 14 a is expressed byFormula 3 recited below.

$\begin{matrix}{\frac{1}{g} = {{- \frac{1}{C}} + \frac{1}{D}}} & \left\lbrack {{Formula}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Here, g is the focal length of the microlens units 14 a, C is thedistance from the object-side principal plane of the microlens units 14a to the virtual imaging point P′70, and D is the distance from theimage-side principal plane of the microlens units 14 a to the opticalimaging points of the microlenses. In such a case, the imagemagnification due to the optical imaging system of the microlens units14 a is expressed by Formula 4 recited below.

$\begin{matrix}{N = \frac{D}{C}} & \left\lbrack {{Formula}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Here, variable E of Formula 5 recited below is introduced from thegeometrical optical relationship. Variable E is a fixed design value inthe case where the optical system is a fixed focus optical system.E=B−C  [Formula 5]

Here, for two adjacent microlens units 14 a, L_(ML) is the arrangementpitch of the microlens units 14 a or the distance between the microlensunits 14 a. In such a case, groups of light rays 84 a, 84 b, 84 c, and86 that are emitted from the same subject are distributed by adjacentmultiple microlens units 14 a to be imaged on the multiple locations ofimage points p1, p2, p3, . . . . Here, L_(ML) and an image shift length^ on one side are expressed by Formula 6 recited below from thegeometrical optical relationship of the chief rays 84 a, 84 b, and 84 cfor each of the microlens units 14 a shown in FIG. 4.

$\begin{matrix}{\frac{C}{L_{ML}} = \frac{D}{\Delta}} & \left\lbrack {{Formula}\mspace{14mu} 6} \right\rbrack\end{matrix}$

From Formula 1, Formula 2, and Formula 6, the shift length Δ of theimage and the distance A from the imaging optical system 12 to thesubject have the relationship shown in Formula 7 recited below.

$\begin{matrix}{A = {\left( {\frac{1}{f} - \frac{1}{B}} \right)^{- 1} = {\left( {\frac{1}{f} - \frac{1}{E + C}} \right)^{- 1} = \left( {\frac{1}{f} - \frac{1}{E + \begin{matrix}{DL}_{ML} \\\Delta\end{matrix}}} \right)^{- 1}}}} & \left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack\end{matrix}$

In Formula 7, f, E, and L_(ML) are parameters of design and are knownfixed values; and Δ and D are determined uniquely from A.

Here, D can be taken to be a fixed value D0 because the change amount ofD is extremely small compared to the change amount of A. D0 is thedistance from the image-side principal plane of the microlens units 14 ato the surface of the solid-state imaging element 16. In such a case,Formula 7 is expressed as Formula 8 recited below.

$\begin{matrix}{A = {\left( {\frac{1}{f} - \frac{1}{B}} \right)^{- 1} = {\left( {\frac{1}{f} - \frac{1}{E + C}} \right)^{- 1} = \left( {\frac{1}{f} - \frac{1}{E + \begin{matrix}{D_{0}L_{ML}} \\\Delta\end{matrix}}} \right)^{- 1}}}} & \left\lbrack {{Formula}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Here, because f, E, D0, and L_(ML) are design values and are known, thesubject distance A is calculatable if the shift length Δ of the imagecan be sensed from the imaging element surface.

Image matching between the images of adjacent microlenses recorded bythe imaging element is used to determine the shift length Δ between theimages when using the imaging lens and the microlenses to image thelight rays emitted from one subject point P at p1, p2, p3, . . . .

For the image matching, a well-known template matching method thatexamines, for example, the degree of similarity and/or the degree ofdissimilarity between two images can be used. Further, when determiningthe shift position more precisely, the shift length can be determinedmore precisely by interpolating the degree of similarity and/or thedegree of dissimilarity obtained for each pixel unit using a continuousfitting function, etc., and determining the subpixel positions where thefitting function is a maximum and a minimum.

Method for Reconstructing Two-Dimensional Image

A method for reconstructing a two-dimensional image without overlap fromthe microlens image groups when the same subject is multiply imaged willnow be described with reference to FIG. 5A to FIG. 5C.

The case is considered where there are three adjacent microlens units 14a; and the three adjacent microlens units 14 a respectively formmicrolens images 91 a, 91 b, and 91 c at the surface of the solid-stateimaging element 16 as shown in FIG. 5B.

Thus, to form the microlens images without overlap, it is sufficient forthe F-number of the imaging optical system 12 and the F-number of themicrolenses to match.

A field of view 93 a, a field of view 93 b, and a field of view 93 c atthe virtual imaging plane 70 are the fields of view where the images 91a, 91 b, and 91 c of the microlenses are imaged and are areas thatoverlap as shown in FIG. 5C. FIG. 5B and FIG. 5C show the case where animage demagnification ratio N is 0.5; and each field of view ismultiplied by 0.5 to be imaged with a relationship such that eachsubject point overlaps two or more times. For the relationship N=0.5,the image at the virtual imaging plane 70 can be reproduced bymultiplying each microlens image by 1/N, i.e., by 2.

The image demagnification ratio N can be known from the microlens imagegroup after the imaging because Formula 9 recited below can be derivedfrom the relationship of Formula 4 and Formula 6.

$\begin{matrix}{N = {\frac{D}{C} = \frac{\Delta}{L_{ML}}}} & \left\lbrack {{Formula}\mspace{14mu} 9} \right\rbrack\end{matrix}$

Because the pitch L_(ML) of the microlenses is known, the imagedemagnification ratio N can be determined by determining the shiftlength Δ of the same subject from the images. The pitch L_(ML) is, forexample, not less than about 10 μm and not more than about 60 μm.

Synthesizing Method for Reconstructing Two-Dimensional Image

The image synthesizing method for reconstructing the two-dimensionalimage will now be described.

FIG. 6A to FIG. 6E illustrate the method for reconstructing thetwo-dimensional image.

FIG. 6A shows a flowchart of the image synthesizing method. FIG. 6Bshows an example of a plenoptic image; FIG. 6C shows an enlargement andarithmetic average example of the pixel signals; FIG. 6D shows anexample of the pixel correspondence of the signals of the pixels; andFIG. 6E shows an example of the two-dimensional image.

First, as shown in FIG. 6A, the output of the plenoptic image (referringto FIG. 6B) from the imaging element is obtained (step S101). Theplenoptic image is, for example, a raw image. The plenoptic imageincludes multiple picture cells (pixels); and each of the multiplepixels corresponds to one selected from mutually-different multiplecolors (e.g., red, green, and blue). Then, white balance processing ofthe plenoptic raw image output from the imaging element is performed toadjust the signal balance of B (blue), G (green), and R (red) (stepS102). In other words, the white balance processing adjusts the signalbalance between the multiple colors.

Continuing, for example, because there is no G and B signal informationat the position of the R pixels, demosaicing is performed to make the Gand B signals by estimating the G and B signals by referring to thepixels disposed around the R pixels (step S103). In other words, forexample, the multiple pixels include a first pixel (a first picturecell) corresponding to a first color (e.g., red). The demosaicingestimates the signal of a second color (e.g., green or blue) of thefirst pixel by referring to the pixels of the multiple pixels disposedaround the first pixel. Although it is sufficient to simply performprocessing to find the average from the surroundings pixels, variousmethods are possible as necessary such as widening the pixel area thatis referred to, etc. (referring to FIG. 6C). The demosaicing isperformed similarly for the G pixels and the B pixels.

Continuing, the image points p1, p2, . . . , pn that correspond to onesubject point P (a first point) such as that shown in FIG. 6D have ann-to-1 correspondence with a signal S′_(p) after the synthesis of thepixel signal values S_(p1), S_(p2), . . . , S_(pn) recorded by theimaging element (step S104). That is, the plenoptic image includes themultiple image points p1, p2, . . . , pn corresponding to the subjectpoint P of the subject. The correspondence between the first point andeach of the multiple image points p1, p2, . . . , pn is calculated instep S104. The correspondence method is performed by sensing therelationship of the image point shift length Δ or the overlaprelationship of the fields of view from the image as described above.

Subsequently, two-dimensional image synthesis is performed (step S105);the two-dimensional image (referring to FIG. 6E) is obtained; and theflow ends. For example, the pixel values of the multiple image pointsp1, p2, . . . , pn are synthesized based on the correspondencecalculated in step S104. Thereby, a post-synthesis signal correspondingto the subject point P is calculated. Thus, the two-dimensional image iscalculated.

The two-dimensional image synthesis will now be described.

FIG. 7 illustrates the arithmetic average.

Here, the pixel signal values S_(p1), S_(p2), . . . , S_(pn) and noisevalues N_(p1), N_(p2), . . . , N_(pn) of the pixels are used in thedescription. First, luminance correction processing of each pixel signalvalue and noise value is performed. Then, luminance correctioncoefficients a₁, a₂, . . . , a_(n) are multiplied respectively by thepixel signal values S_(p1), S_(p2), . . . , S_(pn).

Continuing, the post-synthesis signal value S′_(p) is calculated by thearithmetic average of the values after the multiplications as shown inFormula 10 recited below. Also, the noise value included in thepost-synthesis signal value at this time is as shown in Formula 11.S′ _(p)=(a ₁ ·S _(p1) +a ₂ ·S _(p2) + . . . +a _(n) ·S_(pn))/n  [Formula 10]N′ _(p)=(a ₁ ² ·n _(p1) ² +a ₂ ² ·n _(p2) ² + . . . a _(n) ² ·n _(pn)²)^(0.5) /n  [Formula 11]Relationship between ranging performance and configuration of exit pupil

FIG. 8 shows the heights of light rays passing through the lens crosssections.

FIG. 9 shows the flattening of the exit pupil.

As shown in FIG. 8, the imaging optical system 12 includes the aperturestop S, a first lens L1, a second lens L2, and a third lens L3. Thefirst lens L1 is provided between the aperture stop S and the microlensarray 14. The second lens L2 is provided between the first lens L1 andthe microlens array 14. The third lens L3 is provided between the secondlens L2 and the microlens array 14.

The lens group that includes the first lens L1, the second lens L2, andthe third lens L3 is the main lens. As shown in FIG. 8, in the casewhere a virtual plane 12 p is disposed in the space between the secondlens L2 and the third lens L3 through which off-axis light rays passes,the following definitions are made for the light rays that pass throughthe virtual plane.

For example, off-axis light rays that travel in a direction intersectingthe optical axis Ox are considered. Off-axis light rays L23 include anupper light ray L23 u, a lower light ray L23 d, and a chief ray L23 m.The lower light ray L23 d is positioned between the upper light ray L23u and the optical axis Ox at the virtual plane. The chief ray L23 m ispositioned between the upper light ray L23 u and the lower light ray L23d at the virtual plane.

h(G23iCR) is the height at which the chief ray L23 m of the off-axislight rays passes through the virtual plane.

h(G23iUR) is the height at which the upper light ray L23 u of theoff-axis light rays passes through the virtual plane.

h(G23iDW) is the height at which the lower light ray L23 d of theoff-axis light rays passes through the virtual plane.

The following definitions are made for the chief ray of the off-axislight rays propagating into the page surface.

hx(G23iURX) is the length in the depth direction where the light rayinside the perpendicular plane (passing through the sagittal plane)passes through the virtual plane.

The configuration of an exit pupil EP shown in FIG. 9 is theconfiguration at the virtual plane of the off-axis light rays. Theconfiguration of the exit pupil EP is, for example, treated as anellipse. In such a case, the configuration of the exit pupil EP has afirst diameter and a second diameter. The first diameter is the diameteralong a first direction (the X-direction) in the virtual plane of theexit pupil EP. The second diameter is the diameter along a seconddirection (the Y-direction) in the virtual plane of the exit pupil EP.The following definitions are made for the flattening of the exit pupilEP.

½ times the first diameter is a. In the case where the exit pupil EP istreated as substantially a circle or an ellipse, the first diameter isthe major diameter of the length of the pupil at the exit pupilposition; and a=hx(G23iURX).

½ times the second diameter is b. In the case where the exit pupil EP istreated as substantially a circle or an ellipse, the second diameter isthe minor diameter of the length of the pupil at the exit pupilposition; and b=(hy(G23iUR)−hy(G23iDW))/2.

Flattening p is defined as ρ=|1−b/a| for the radius a and the radius b.

The uniformity of the group of light rays passing through the exit pupilEP is important for the relationship between the flattening and theranging performance. As shown in FIG. 8, for higher ranging precision,it is important to design so that the proportion of b′/b″ to b/bapproaches 1, where the position proportion of the light rays grouppassing through the aperture stop (the aperture stop S) is b/b.

At the optical axis vicinity, the change of the proportion of b′/b″ tob/b is small; and problems due to distortion do not occur easily. On theother hand, at positions having high angles of view, the change of theproportion of b/b″ to b/b is large; and ranging errors due to thedistortion occur easily. Therefore, it is necessary for the circularcross section of the group of light rays not to flatten or to have auniform interior as much as possible from the optical axis vicinity topositions having high angles of view.

Formulas and Parameters of Lens Configuration

In the following description, the optical axis direction of the lens istaken as the Z-direction; one normal direction of the optical axis istaken as the Y-direction; and a direction orthogonal to the Z-directionand the Y-direction is taken as the X-direction. The positive directionof the Z-direction is the direction from the object side of the mainlens group toward the image plane.

Counting from the object side, the curvature radius of the ith surface(including the aperture stop surface) is Ri; the surface spacing alongthe optical axis between the ith and (i+1)th surfaces is Di; andcounting from the object side, the refractive index and Abbe number ofthe jth lens are nj and vj, respectively.

$\begin{matrix}{z = {\frac{{cY}^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)c^{2}Y^{2}}}} + {a_{4}Y^{4}} + {a_{6}Y^{6}} + \ldots + {a_{20}Y^{20}}}} & \left\lbrack {{Formula}\mspace{14mu} 12} \right\rbrack\end{matrix}$

In Formula 12, c is the curvature of the aspherical surface vertex, K isthe conic constant, aI is the aspherical constant, Y is the height fromthe optical axis, and Z is the distance from the tangent plane to thepoints on the aspherical surface at the lens surface vertex.

Lens Configuration

A specific lens configuration will now be described.

FIG. 10 illustrates the configuration of the imaging lens according tothe embodiment.

As shown in FIG. 10, the imaging lens 110 includes the microlens arrayMLA (14) and the imaging optical system 12 which is the first opticalsystem. In FIG. 10, S is the aperture stop, R1 is a surface (a firstsurface) on the object side of the first lens L1, R2 is a surface (asecond surface) on the image side of the first lens L1, R3 is a surface(a third surface) on the object side of the second lens L2, R4 is asurface (a fourth surface) on the image side of the second lens L2, R5is a surface (a fifth surface) on the object side of the third lens L3,R6 is a surface (a sixth surface) on the image side of the third lensL3, R7 is a surface (a seventh surface) on the object side of coverglass CG, R8 is a surface (an eighth surface) on the image side of thecover glass CG, R9 is a surface (a ninth surface) on the object side ofthe microlens array MLA, R10 is a surface (a tenth surface) on the imageside of the microlens array MLA, and DT is the imaging plane of thesolid-state imaging element 16. The imaging plane is the plane in whichthe multiple pixels are provided.

The first surface R1 opposes the aperture stop S. The second surface R2is provided between the first surface R1 and the microlens array 14.

The third surface R3 opposes the second surface R2. The fourth surfaceR4 is provided between the third surface R3 and the microlens array MLA(14).

The fifth surface R5 opposes the fourth surface R4. The sixth surface R6is provided between the fifth surface R5 and the microlens array MLA(14).

The imaging lens 110 according to the embodiment can acquire both ahigh-precision range image and a good visible image.

The imaging optical system 12 includes the aperture stop S, the firstlens L1 having a positive refractive power, the second lens L2 having anegative refractive power, and the third lens L3 having a positiverefractive power that are disposed in this order from the object sidetoward the image plane side. The lens group that includes the first lensL1, the second lens L2, and the third lens L3 is the main lens.

The microlens array MLA (14) and the solid-state imaging element 16 aredisposed on the image side of the imaging optical system 12.

The microlens array MLA (14) is disposed between the imaging opticalsystem 12 and the solid-state imaging element 16 including the multiplepixels. The microlens array MLA (14) is provided between the imagingoptical system 12 and the focal position of the imaging optical system12. In other words, the microlens array MLA (14) is disposed on theobject side of the focal position of the imaging optical system 12. Themicrolens array MLA (14) includes the multiple microlens units 14 a. Onemicrolens unit 14 a overlaps two or more pixels as viewed from theoptical axis direction. Each of the multiple microlens units 14 aoverlaps at least two pixels of the multiple pixels 16 b when projectedonto the first plane 14 p.

In the embodiment, the main lens may include a lens that substantiallydoes not have power. Also, the entire lens configuration may include alens (e.g., the cover glass CG) that substantially does not have power.

Here, the orientations of the lenses of the main lens which is made ofthree lenses are as follows.

The curvature radius of the surface (the first surface) on the objectside of the first lens L1 is positive.

The curvature radii of the surface (the third surface) on the objectside of the second lens L2 and the surface (the fourth surface) on theimage side of the second lens L2 both are negative.

The curvature radii of the surface (the fifth surface) on the objectside of the third lens L3 and the surface (the sixth surface) on theimage side of the third lens L3 both are positive.

It is desirable for the arrangement between the imaging optical system12 and the microlens array MLA (14) to be such that a demagnificationratio Nf when the microlens array MLA (14) demagnifies the image passingthrough the imaging optical system 12 is not less than 0.001 and notmore than 0.87.

Thus, the basic configuration of the main lens is made of the positivefirst lens L1, the negative second lens L2, and the positive third lensL3 and has a triplet lens configuration. By such a configuration, a thinimaging lens 110 having an appropriate backfocus and a short total lenslength is obtained.

The number of lenses of the main lens is set to be three as a result ofconsidering the performance as the highest priority and size reductionas a priority. In the case where the number of lenses of the main lensis two or less, it is difficult to reduce the field curvature; and theperipheral performance degrades. The performance is better in the casewhere the number of lenses of the main lens is three or more. On theother hand, the total length increases, which may cause the weight toincrease. Accordingly, the size of the main lens is reduced and goodperipheral performance is provided by using a three-lens configurationin which it is possible to reduce the field curvature and distortionaberration.

It is desirable for at least one surface of the surfaces (R1 to R6) ofthe first lens L1, the second lens L2, and the third lens L3 included inthe main lens to be an aspherical surface. Also, it is desirable for onesurface on at least one selected from the object side and the imageplane side to be an aspherical surface.

By using an aspherical surface in the positive first lens L1, using anaspherical surface having a negative refractive power in the second lensL2, and using an aspherical surface having a positive refractive powerin the third lens L3, an imaging lens can be obtained in which variousaberrations and particularly astigmatic aberration and distortionaberration are corrected, the total length of the lens system is short,and the imaging magnification of the imaging on the imaging plane DT ofthe solid-state imaging element 16 has a demagnification ratio for anincident angle on the microlens array MLA (14) of 30 degrees or less.

Further, by employing an aspherical surface in the second lens L2 havinga negative refractive power and by appropriately disposing the spacingbetween the first lens L1 and the second lens L2 and the spacing betweenthe second lens L2 and the third lens L3, various aberrations (comaticaberration, astigmatic aberration, and distortion aberration) of thescreen peripheral portion distal to the optical axis can be corrected byutilizing the difference occurring between the transmission heights ofthe on-axis ray and the marginal ray.

It is desirable for the first lens L1 to be made of a glass material ora plastic material and for the second lens L2 and the third lens L3 tobe made of a plastic material. Lenses that include a glass material anda plastic material also include lenses in which the surface of theplastic material is coated to prevent reflections and increase surfacehardness.

The lens is small; and in the production of small lenses, plasticmaterials can be manufactured by injection molding, etc., and are moresuitable to mass production than are glass materials. Further, plasticlenses are suitable to mass production with low manufacturing costs.

The aperture stop S adjusts the subject light amount passing through themicrolens array MLA (14) and reaching the solid-state imaging element16. The aperture stop S is disposed on the object side of the main lens.In other words, the aperture stop S, the first lens L1, the second lensL2, and the third lens L3 are disposed in the imaging lens 110 in orderfrom the object side.

In the imaging lens 110, the incident angle onto the microlens array MLA(14) is reduced because the aperture stop S is disposed furthest on theobject side. That is, the distance from the imaging plane to the exitpupil position can be longer for the type in which the aperture stop Sis disposed furthest on the object side than for a middle-stop type inwhich the aperture stop is provided between the first lens L1 and thethird lens L3.

In the case where the exit pupil is distal to the imaging plane, thechief ray of the light rays emitted from the final surface of theimaging lens 110 is incident on the microlens array MLA (14) at an anglethat is nearly perpendicular, that is, the shift between the exit pupilof the imaging lens 110 and the exit pupils of the single lenses (themicrolens units 14 a) of the microlens array MLA (14) can be reduced;and good aberration performance can be ensured.

The microlens array MLA (14) is disposed between the imaging opticalsystem 12 and the solid-state imaging element 16. The image that passesthrough the microlens array MLA (14) is imaged on the solid-stateimaging element 16 as a virtual image and is imaged at a demagnificationratio. Thereby, the original central performance and peripheralperformance of the imaging lens 110 can be corrected to be even better.

Microlens Array

The microlens array MLA applied to the imaging lens 110 will now bedescribed.

FIG. 11 is a schematic plan view illustrating the arrangement of themicrolens units.

FIG. 12 to FIG. 13 are ray diagrams of the microlenses.

As shown in FIG. 11, the microlens array MLA (14) has a lens opticalsystem arrangement using the multiple microlens units 14 a. The lensoptical system arrangement is such that the light in the axis directionof each of the microlens units 14 a reaches the same position of eachsegment for each field of view. In the multiple optical systemarrangement, the multiple optical systems are disposed uniformly fromthe center of the multiple optical system arrangement and are disposed,for example, in a hexagonal arrangement such as that shown in FIG. 11.In the case where the multiple microlens units 14 a are packed in ahexagonal arrangement without gaps, the configuration of the outercircumference of each of the microlens units 14 a is a hexagon.

The microlens array MLA (14) is formed of a refractive optical system.The microlens array MLA (14) is disposed between the imaging opticalsystem 12 and the solid-state imaging element 16; and the imaging on theimaging element is at a virtual image magnification. The microlens arrayMLA (14) images light rays from the imaging optical system 12 havingdifferent angles of view on the solid-state imaging element 16. Becausethe microlens units 14 a that are inside the microlens array MLA (14)are disposed in a hexagonal arrangement, the incident angle on themicrolens unit 14 a at the field-of-view periphery increases as theangle of view increases.

FIG. 12 shows a ray diagram when chief rays from the imaging opticalsystem 12 are incident on the microlens array MLA (14) at an angle of 0degrees.

FIG. 13 shows a ray diagram when chief rays from the imaging opticalsystem 12 are incident on the microlens array MLA (14) at an angle of 30degrees.

The refractive optical system that is formed in the microlens array MLA(14) is disposed between the imaging optical system 12 and thesolid-state imaging element 16 at the appropriate virtual imagemagnification and is configured to have the appropriate focal length andF-number so that the light rays outside the field of view from theimaging optical system 12 can reach the imaging element as efficientlyas possible.

In the imaging lens 110 according to the embodiment, the focal lengthand F-number of the microlens units 14 a of the microlens array MLA (14)are set so that the light rays for which the incident angle of the chiefrays on the image side are within 20 degrees to 30 degrees canefficiently reach the solid-state imaging element 16. As an example,Table 1 shows the specifications of a single lens (one microlens unit 14a) of the microlens array MLA (14) that images with a virtual imagemagnification of 0.5 times.

The parameters recited in Table 1 mean the following.

Nd is the d-line (587.6 nanometers (nm)) refractive index of the opticalmaterial of the lens.

νd is the Abbe number of the optical material of the lens for thed-line.

R is the effective radius (the millimeters (mm)), i.e., the radius ofthe circular region through which the light rays passes.

f is the focal length (mm).

TABLE 1 fd (d-LINE FOCAL DISTANCE) 0.068 mm (d-LINE WAVELENGTH λ: 587.56nm) F -NUMBER 2.2 EFFECTIVE APERTURE DIAMETER Φ 0.030 mm RADIAL SURFACENUMBER THICKNESS MATERIAL 0 (OBJECT SURFACE) −0.05 AIR 1 (APERTURE STOP)INFINITY SYNTHETIC QUARTZ (∞) 0.15 (Nd = 1.45844) 2 −0.03536 AIR 3(IMAGE PLANE) INFINITY AIR

FIG. 14 is a ray diagram of a microlens.

FIG. 14 is the ray diagram of a single lens of the microlens array MLAshown in Table 1 for a chief ray angle of 0 degrees.

FIG. 15 shows aberration curves of the microlens.

FIG. 15 is the aberration diagram (for the chief ray angle of 0 degrees)of the single lens of the microlens array MLA shown in Table 1.

FIG. 16 is a ray diagram of the microlens.

FIG. 16 is the ray diagram of the single lens of the microlens array MLAshown in Table 1 for a chief ray angle of 20 degrees.

FIG. 17 shows aberration curves of the microlens.

FIG. 17 is the aberration diagram (for the chief ray angle of 20degrees) of the single lens of the microlens array MLA shown in Table 1.

FIG. 18 is a ray diagram of the microlens.

FIG. 18 is the ray diagram of the single lens of the microlens array MLAshown in Table 1 for a chief ray angle of 30 degrees.

FIG. 19 shows aberration curves of the microlens.

FIG. 19 is the aberration diagram (for a chief ray angle of 30 degrees)of the single lens of the microlens array MLA shown in Table 1.

Condition Formulas of First Optical System (Imaging Optical System 12)

Condition Formulas of the imaging optical system 12 will now bedescribed.

As shown in FIG. 10, the imaging lens 110 according to the embodimentincludes, in order from the object side toward the image plane side, theaperture stop S, the first lens L1 that has a positive refractive powerand a configuration in which the curvature radius of the surface on theobject side is positive, the second lens L2 that has a negativerefractive power and a configuration in which the curvature radii of theobject-side surface and the image-side surface both are negative, andthe third lens L3 that has a positive refractive power and is formed ina configuration in which the curvature radii of the object-side surfaceand the image-side surface both are positive; and the microlens arrayMLA (14) and the solid-state imaging element 16 are disposed rearward ofthese lenses.

In the imaging lens 110, the microlens array MLA (14) is disposedbetween the imaging optical system 12 and the solid-state imagingelement 16. It is desirable for the magnification to be not less than0.001 and not more than 0.87 in the case where the image formed by theimaging optical system 12 is to be demagnified by the microlens arrayMLA (14).

In such an optical system, the imaging lens 110 satisfies ConditionFormulas (1) to (6) recited below.0.6<f1/f<0.9  (1)1.0<|f2|/f<3.0  (2)2.0<f3/f<200  (3)TL/f<1.3  (4)0<D2/f<0.2  (5)0<D5/f<0.5  (6)

In Condition Formulas (1) to (6) recited above, f is the focal length ofthe entire system of the imaging optical system 12, f1 is the focallength of the first lens L1, f2 is the focal length of the second lensL2, f3 is the focal length of the third lens L3, TL is the distancebetween the aperture stop S and the imaging plane DT (the solid-stateimaging element 16), D2 is the distance along the optical axis Oxbetween the second lens L2 and the third lens L3, and D5 is thethickness along the optical axis Ox of the third lens L3.

The basic characteristics of the lens configuration of the imaging lens110 of the embodiment are made of the first lens which has the largepositive power, the second lens L2 which has the relatively largenegative power, and the third lens L3 which has the small positive poweron the side most proximal to the image; and the power arrangement is aso-called positive-negative-positive triplet-type.

Further, the imaging lens 110 has the characteristic of performingachromatization to correct the chromatic aberration by the first lens L1which has the large power, the second lens L2, and the third lens L3.

Accordingly, the first lens L1 and the second lens L2 have the effect ofmainly correcting the spherical aberration, the comatic aberration, andthe chromatic aberration proximal to the optical axis; and the thirdlens L3 has the effect of mainly correcting the distortion aberration,which is an off-axis aberrations, and maintaining good telecentricity.

Condition Formulas (1), (2), and (3) regulate the optimal refractivepower arrangement for obtaining good optical performance in an imaginglens including few lenses.

Condition Formula (1) is a condition formula relating to the power ofthe first lens L1 for the combined focal length of the entire lenssystem. In the case where the power of the first lens L1 increases andthe conditions are below the lower limit of Condition Formula (1), thecomatic aberration and spherical aberration of the upper light ray, thecomatic aberration, and the chromatic aberration become large; theperformance undesirably degrades; correction is difficult; and thecontrast of the entire screen decreases. Also, the curvature radius ofthe spherical surface of the lens of the first lens L1 becomes small;and the patterning is difficult.

On the other hand, in the case where the power of the first lens L1decreases and the upper limit of Condition Formula (1) is exceeded, thebackfocus becomes long; the total length of the lens system becomeslarge; compactness is lost; the comatic aberration of the light raysbecomes large; and the performance undesirably degrades. Accordingly, itis difficult to reduce the total length of the imaging lens 110.

In Condition Formula (1), it is more favorable for the range to be0.6<f1/f<0.8, and even more favorable for the range to be 0.7<f1/f<0.8.

Condition Formula (2) recited above is a condition formula relating tothe absolute value of the power of the second lens L2 for the combinedfocal length of the entire lens system. Condition Formula (2) regulatesthe negative power of the second lens L2. It is necessary for the powerof the negative second lens L2 to correct the aberration occurring dueto the positive lens of the first lens L1. In the case where thenegative power of the second lens L2 is set to be strong, theperformance undesirably degrades because the negative power is excessivewith respect to the correction effect of the negative lens. Inparticular, the chromatic aberration at the optical axis and thechromatic aberration of the magnification degrade. Moreover, theincident angle onto the imaging plane becomes too large. Therefore, itis favorable to set the negative power of the second lens L2 to berelatively weak. Accordingly, it is favorable to satisfy ConditionFormula (2).

In the case where the power of the second lens L2 is strong and theconditions are below the lower limit of Condition Formula (2), the totallength becomes long; the light ray height of the peripheral light raysbecomes high; correction of the astigmatic aberration is difficult; andthe contrast of the entire screen decreases. Moreover, the curvatureradius of the spherical surface of the lens of the second lens L2becomes small; and the patterning is difficult. Further, the incidentangle onto the solid-state imaging element 16 becomes large; and it isunfavorably difficult to ensure the telecentric characteristics on theimage plane side.

In the case where the upper limit of Condition Formula (2) is exceeded,the aberration correction balance of the on-axis aberrations and theoff-axis aberrations degrades; and the off-axis aberrations cannot becorrected easily.

In Condition Formula (2), it is more favorable for the range to be1.0<|f2|/f<2.5, and even more favorable for the range to be1.5<|f2|/f<2.5.

Condition Formula (3) is a condition formula for regulating therefractive power of the positive third lens L3. Condition Formula (3)provides the balance between the refractive power of the positive firstlens L1 and the refractive power of the negative second lens L2. In thecase where the balance between the power of the first lens L1 and thepower of the second lens L2 degrades, the total length of the imagingoptical system increases or the performance undesirably degrades.

In the case where the power of the third lens L3 is large and theconditions are below the lower limit of Condition Formula (3), this isadvantageous for size reduction, but it is difficult to correct thetelecentricity and distortion aberration of the peripheral portion.Moreover, good performance cannot be ensured because the astigmaticaberration is under-corrected.

In the case where the power of the third lens L3 is small and the upperlimit of Condition Formula (3) is exceeded, the power of the positivethird lens L3 becomes too weak; the incident angle onto the solid-stateimaging element 16 undesirably becomes too large; and the correction ofthe comatic aberration and the astigmatic aberration is insufficient.The backfocus of the entire lens system undesirably becomes long, whichis disadvantageous for the reduction of the total length of the imagingoptical system.

In Condition Formula (3), it is more favorable for the range to be2.0<f3/f<150, and even more favorable for the range to be 2.0<f3/f<100.

Condition Formula (4) regulates the total length of the lens system ofthe imaging optical system 12. In the case where the upper limit ofCondition Formula (4) is exceeded, compactness is not possible becausethe total lens length becomes large. Accordingly, according to theconfiguration satisfying Condition Formula (4), it is easy to make theimaging lens smaller and thinner.

In Condition Formula (4), it is more favorable when f/TL<1.2, and evenmore favorable when f/TL<1.0.

Condition Formula (5) is a condition formula for regulating the spacingbetween the second lens L2 and the third lens L3. In the case where theupper limit of Condition Formula (5) is exceeded, the aberrationcorrection balance between the on-axis aberrations and the off-axisaberrations degrades; and the off-axis aberrations cannot be correctedeasily. On the other hand, when the conditions are below the lower limitof Condition Formula (5), the peripheral performance degrades because alarge field curvature occurs and the astigmatic aberration is notcorrected sufficiently.

In Condition Formula (5), it is more favorable for the range to be0<D2/f<0.15, and even more favorable for the range to be 0<D2/f<0.10.

Condition Formula (6) is a condition formula for regulating thethickness along the optical axis of the third lens L3. In the case wherethe upper limit of Condition Formula (6) is exceeded, the aberrationcorrection balance between the on-axis aberrations and the off-axisaberrations degrades; and the magnification chromatic aberration cannotbe corrected easily. Moreover, the chromatic aberration at the peripherycannot be corrected easily when combining with a MLA lens because theexit pupil configuration of the off-axis light rays greatly deforms.

In Condition Formula (6), it is more favorable for the range to be0<D5/f<0.4, and even more favorable for the range to be 0<D5/f<0.3.

Also, in the imaging lens 110 according to the embodiment, it isdesirable for the height position of the chief ray passing through thesecond lens L2 to satisfy Condition Formula (7) recited below.0.3<hc(G2R)D(D1+D2+D3)<0.6  (7)

In Condition Formula (7), hc(G2R) is the height at which the chief rayof the off-axis light rays of the maximum angle of view passes throughthe surface (the fourth surface) on the image side of the second lensL2. In other words, hc(G2R) is the distance between the optical axis Oxand the position where the chief ray of the off-axis light rays and thefourth surface intersect. D1+D2+D3 is the distance along the opticalaxis Ox from the aperture stop S to the surface (the fourth surface) onthe image side of the second lens L2. D1 is the thickness along theoptical axis Ox of the first lens L1. D2 is the air space along theoptical axis Ox between the first lens L1 and the second lens L2. Inother words, D2 is the product of the distance along the optical axis Oxbetween the first lens L1 and the second lens L2 and the refractiveindex of the region between the first lens L1 and the second lens L2. D3is the thickness along the optical axis Ox of the second lens L2.

Here, Condition Formula (7) is a condition formula for controlling theheight at which the off-axis chief ray passes through the second lensL2. Condition Formula (7) is the condition for preventing the occurrenceof the chromatic aberration as much as possible when the off-axis lightrays that pass through the imaging lens 110 are incident on themicrolens array MLA (14); and Condition Formula (7) limits theconfiguration of the exit pupil of the off-axis light rays.

In the case where the upper limit of Condition Formula (7) is exceededand the height at which the chief ray of the off-axis light rays of themaximum angle of view passing through the surface (the fourth surface)on the image side of the second lens L2 becomes high, the incidentheight on the surface (the fifth surface) on the object side of thethird lens L3 becomes high; and it is necessary to relax the refractivepower of the surface (the fifth surface) on the object side of the thirdlens L3. Although the occurrence of the comatic aberration increasesbecause the refractive power of this portion is weakened, theconfiguration of the exit pupil of the off-axis light rays does notchange greatly.

In the case where the conditions are below the lower limit of ConditionFormula (7), the light ray height at the surface (the fifth surface) onthe object side of the third lens L3 decreases; and it is necessary toincrease the refractive power of the light rays at the third lens L3.Because the refractive power of this portion is increased, it isdifficult to ensure the incident angle of the light rays toward theprescribed image height, i.e., the CRA (Chief Ray Angle (the incidentangle of the chief ray onto the image plane)). Because it is necessaryto increase the negative refractive power of the second lens L2 toensure the incident height on the third lens L3, a large comaticaberration of the off-axis light rays occurs; and the configuration ofthe exit pupil of the off-axis light rays undesirably changes greatly.

In Condition Formula (7), it is more favorable for the range to be0.3<hc(G2R)/D(D1+D2+D3)<0.5, and even more favorable for the range to be0.3<hc(G2R)D(D1+D2+D3)<0.4.

The configuration of the exit pupil is the configuration of the off-axislight rays at the exit pupil plane of the imaging optical system 12. Theexit pupil plane is, for example, the plane at which the exit pupil ofthe imaging optical system 12 is imaged. The configuration of the exitpupil is, for example, treated as an ellipse. In such a case, theconfiguration of the exit pupil has a first diameter and a seconddiameter. The first diameter is the diameter along the first direction(the X-direction) in the exit pupil plane of the exit pupil. The seconddiameter is the diameter along the second direction (the Y-direction) inthe exit pupil plane of the exit pupil.

In the imaging lens 110 according to the embodiment, it is desirable forthe exit pupil configuration at the position of the exit pupil tosatisfy Condition Formula (8) recited below.0≦ρ<0.3  (8)

In Condition Formula (8), p is the flattening. The flattening ρ isρ=|1−b/a|. a is the radius in the first direction orthogonal to theoptical axis of the off-axis light rays passing through the exit pupilat the exit pupil position. b is the radius in the second direction (thedirection orthogonal to the first direction) orthogonal to the opticalaxis of the off-axis light rays passing through the exit pupil at theexit pupil position.

a is ½ times the first diameter. When the exit pupil is treated assubstantially a circle or an ellipse, the first diameter is the majordiameter of the length of the pupil at the exit pupil position. Theradius a is expressed by a=hx(EXTPURX).

b is ½ times the second diameter. When the exit pupil is treated assubstantially a circle or an ellipse, the second diameter is the minordiameter of the length of the pupil at the exit pupil position. Theradius b is expressed by b=(hy(EXTPiUR)−hy(EXTPiDW))/2.

h(EXTPiCR) is the height at which the chief ray of the off-axis lightrays passes through the exit pupil plane.

h(EXTPiUR) is the height at which the upper light ray of the off-axislight rays passes through the exit pupil plane.

h(EXTPiDW) is the height at which the lower light ray of the off-axislight rays passes through the exit pupil plane.

hx(EXTPURX) is the length in the depth direction of the light rays inthe plane perpendicular to the chief ray of the off-axis light rays thatpass through the exit pupil plane. hx(EXTPURX) is ½ times the lengthalong the first direction (the X-direction) of the off-axis light raysL23 in the exit pupil plane.

For example, hy(EXTPiUR) is the height in the second direction at whichthe upper light ray of the off-axis light rays passes through the exitpupil plane. hy(EXTPiUR) is the distance along the second direction (theY-direction) between the optical axis Ox and the position where theupper light ray L23 u passes through the exit pupil plane. hy(EXTPiDW)is the height in the second direction at which the lower light ray ofthe off-axis light rays passes through the exit pupil plane. hy(EXTPiDW)is the distance along the second direction between the optical axis Oxand the position where the lower light ray L23 d passes through the exitpupil plane.

Condition Formula (8) is the condition formula for the configuration ofthe exit pupil at the position of the exit pupil of the imaging lens 110according to the embodiment.

When the light rays from the imaging optical system 12 is demagnifiedand imaged onto the solid-state imaging element by the microlens arrayMLA (14), it is ideal for the configuration of the exit pupil of theimaging optical system 12 and the configuration of the entrance pupil ofthe single lens on the microlens array MLA (14) to match so that thelight rays efficiently reaches the solid-state imaging element 16.

However, actually, because the arrangement of the single lenses of themicrolens array MLA (14) has hexagonal packing density, even if singlelens centers on the microlens array MLA (14) are aligned with the centerof the solid-state imaging element 16, the chief ray of the off-axislight rays that has a large angle of view has a large incident anglewith respect to the optical axes of the single lenses of the microlensarray MLA (14) and is incident at a tilt of 20 degrees to 30 degreeswith respect to the optical axis of the microlens array MLA (14); andtherefore, it is difficult to align the entrance pupil position of themicrolens array MLA (14) and the exit pupil position of the imagingoptical system 12.

The pupil configuration of the off-axis light rays that is emittedtilted with respect to the imaging optical system 12 is an ellipse (aconfiguration such as a laterally-long cat's eye) due to the effect ofvignetting. To cause the off-axis light rays from the imaging opticalsystem 12 to be incident efficiently on the single lenses of themicrolens array MLA (14) as much as possible, it is necessary for theconfiguration of the exit pupil from the imaging optical system 12 to bea configuration as close to a circle as possible. Condition Formula (8)regulates such a pupil configuration.

In the case where the upper limit of Condition Formula (8) is exceeded,the configuration of the exit pupil of the imaging optical system 12shifts greatly from the configuration of the exit pupil of the singlelenses of the microlens array MLA (14). Therefore, it is difficult tocause the light rays to pass through the microlens array MLA (14) andefficiently reach the solid-state imaging element 16.

In Condition Formula (8), it is more favorable for the range to be0≦ρ<0.2, and even more favorable for the range to be 0≦ρ<0.15.

In the imaging lens 110 according to the embodiment, it is desirable forCondition Formula (9) recited below to be satisfied.0≦ν−ν2  (9)

In Condition Formula (9), ν1 is the Abbe number of the first lens L1;and ν2 is the Abbe number of the second lens L2.

Condition Formula (9) regulates the Abbe numbers of the materialsincluded in the positive first lens L1 and the negative second lens L2.By satisfying Condition Formula (9), it is possible to correct thechromatic aberration at the optical axis and the off-axis chromaticaberration of the magnification.

The imaging lens 110 according to the embodiment may be configured tosatisfy Condition Formula (10) recited below.20°≦αi≦30°  (10)

In Condition Formula (10), αi is the incident angle of the chief ray ofthe off-axis light rays onto the imaging plane DT at the maximum angleof view (the maximum image height).

In the imaging lens 110 according to the embodiment, in the case wherethe solid-state imaging element 16 and the microlens array MLA (14) areused in combination, when the off-axis light rays that is emitted fromthe imaging optical system 12 is incident at a large angle with respectto the microlens array MLA (14) and passes through the microlens arrayMLA (14) to be imaged on the solid-state imaging element 16, the angleof view of the off-axis light rays that can be tolerated by themicrolens array MLA (14) undesirably shifts greatly; and the brightnessof the image is undesirably different between the image central portionand the image peripheral portion. When the incident angle on themicrolens array MLA (14) is small, this problem is reduced, but thetotal length of the optical system undesirably becomes large. Therefore,it is favorable to satisfy Condition Formula (10).

Thus, according to the imaging lens 110 of the embodiment and the solidstate imaging device 1 that includes the imaging lens 110, a low numberof lenses and a simple lens configuration are possible; high performancesuch as the F-number being small, etc., can be achieved; and the lenssystem itself can be compact. Also, both a high-precision range imageand a good visible image can be acquired.

The imaging lens 110 and the solid state imaging device 1 according tothe embodiment are applicable to various electronic devices such as, forexample, a portable terminal such as a mobile telephone, a tabletterminal, a digital camera, or the like, a video device, an industrialrobot, a robot arm, a medical device such as an endoscope, etc.

A numerical example of the imaging optical system 12 will now bedescribed as an example.

First Example

FIG. 20 illustrates the configuration of an imaging lens according to afirst example.

FIG. 21 and FIG. 22 are various aberration diagrams of the imaging lensaccording to the first example.

FIG. 23 illustrates the exit pupil position of the imaging lensaccording to the first example.

FIG. 24 illustrates the configurations and numerical values of the exitpupils of the imaging lens according to the first example.

Table 2 recited below illustrates the curvature radius Ri, the spacingDi, the refractive index nd, and the dispersion value νd for thesurfaces of the imaging optical system 12 according to the firstexample.

TABLE 2 f 4.56 mm F-NUMBER = 2.24 ω = 32° SURFACE Ri Di nd νd (APERTUREINFINITY 0.00000 STOP(s) 1 1.56915 1.08739 1.52528 55.95 2 6.388560.47016 3 −2.31466  0.39136 1.61421 25.58 4 −5.17862  0.42580 5 3.247131.25821 1.52528 55.95 6 3.76960 0.33796    7 (CG) INFINITY 0.300001.51680 64.17 8 INFINITY 0.50000    9 (MLA) INFINITY 0.15000 1.1584167.83 10  INFINITY 0.30000

The following is the aspherical surface data of the imaging opticalsystem 12 according to the first example.

First surface:

K=−0.20635

a4=0.0026523617

a6=0.0007572847

a8=0.0291724751

a10=−0.088437280

a12=0.0936050540

a14=−0.037365195

Second surface:

K=−26.44687

a4=−0.019607836

a6=−0.059941816

a8=0.0683856688

a10=−0.23123545

a12=0.1976539207

a14=−0.055919811

Third surface:

K=−1.07394

a4=−0.186694844

a6=−0.209825776

a8=0.6492044946

a10=−0.648835892

a12=−0.527660809

a14=1.5596893775

a16=−0.812155745

Fourth surface:

K=10.90861

a4=−0.257661814

a6=0.2041165409

a8=−0.066789470

a10=0.0058690518

a12=0.0254239177

a14=0.0371547120

a16=−0.019455088

Fifth surface:

K=−16.94786

a4=−0.56635536

a6=0.670840323

a8=−1.47204909

a10=1.549708682

a12=0.150886336

a14=−1.06494220

a16=−0.72016649

a18=1.717681955

a20=−0.65311677

Sixth surface:

K=−6.37821

a4=−0.1369577

a6=−0.02239878

a8=0.033002391

a10=−0.01986092

a12=0.008995937

a14=−0.000399589

a16=0.001095174

a18=−0.00012917

a20=−0.00000215

f1/f=0.801

|f2|/f=1.561

f3/f=5.311

f/TL=1.121

D2/f=0.093

D5/f=0.276

hc(G2R)/(D1+D2+D3)=0.418

ν1−ν2=30.37

ρ=0.163

CRA (incident angle of chief ray onto image plane) (angle of view of 31degrees)=27.168°.

As described below, Condition Formulas (1) to (10) recited above aresatisfied in the example. As recited above, it can be seen that theimaging optical system 12 according to the first example has goodperformance.

Second Example

FIG. 25 illustrates the configuration of an imaging lens according to asecond example.

FIG. 26 and FIG. 27 are various aberration diagrams of the imaging lensaccording to the second example.

FIG. 28 illustrates the exit pupil position of the imaging lensaccording to the second example.

FIG. 29 illustrates the configurations and numerical values of the exitpupils of the imaging lens according to the second example.

Table 3 recited below shows the curvature radius Ri, the spacing Dic,the refractive index nd, and the dispersion value νd for the surfaces ofthe imaging optical system 12 according to the second example.

TABLE 3 f 4.59 mm F-NUMBER = 2.24 ω = 32.03° SURFACE Ri Di nd νd(APERTURE INFINITY 0.00000 STOP(s) 1 1.489118 0.82969 1.54413 55.98 24.730869 0.55525 3 −2.670959  0.39136 1.61421 25.58 4 −5.242258  0.477145 4.805683 1.29150 1.54413 65.98 6 4.431227 0.53605    7 (CG) INFINITY0.30000 1.51680 64.17 8 INFINITY 0.30000    9 (MLA) INFINITY 0.150001.45844 67.83 10  INFINITY 0.31326

The aspherical surface data of the imaging optical system 12 accordingto the second example is as follows.

First surface:

K=−0.38494

a4=0.0171071031

a6=0.0036350659

a8=0.0363451319

a10=−0.085885467

a12=0.0917809567

a14=−0.034697572

a16=−0.000087116

Second surface:

K=14.26463

a4=−0.015181501

a6=−0.019061020

a8=0.0440043763

a10=−0.145180982

a12=0.1838550056

a14=−0.101532532

Third surface:

K=0.84715

a4=−0.105398051

a6=−0.095650008

a8=0.5354757811

a10=−0.652596321

a12=−0.164674543

a14=0.9793333945

a16=−0.606186909

Fourth surface:

K=4.05765

a4=−0.167280149

a6=0.1612834476

a8=−0.036538152

a10=0.0077283823

a12=0.0091569156

a14=0.0138977112

a16=−0.00545494

Fifth surface:

K=−83.08277

a4=−0.36728695

a6=0.318695236

a8=−1.06102987

a10=1.371938273

a12=0.013873971

a14=−0.99872086

a16=−0.61335553

a18=1.68667291

a20=−0.67437564

Sixth surface:

K=−32.8186

a4=−0.0721218

a6=−0.06358615

a8=0.037227031

a10=−0.00605082

a12=−0.00148953

a14=−0.00135596

a16=0.001342416

a18=−0.00036955

a20=0.000031273

f1/f=0.794

|f2|/f=2.033

f3/f=103.683

TL/f=1.096

D2/f=0.104

D5/f=0.281

hc(G2R)/(D1+D2+D3)=0.467

ν1−ν2=30.37

ρ=0.179

CRA (incident angle of chief ray onto image plane) (angle of view of 31degrees)=26.12°.

As described below, Condition Formulas (1) to (10) recited above aresatisfied in the example. As recited above, it can be seen that theimaging optical system 12 according to the second example has goodperformance.

Third Example

FIG. 30 illustrates the configuration of an imaging lens according to athird example.

FIG. 31 and FIG. 32 are various aberration diagrams of the imaging lensaccording to the third example.

FIG. 33 illustrates the exit pupil position of the imaging lensaccording to the third example.

FIG. 34 illustrates the configurations and numerical values of the exitpupils of the imaging lens according to the third example.

Table 4 recited below shows the curvature radius Ri, the spacing Dic,the refractive index nd, and the dispersion value νd for the surfaces ofthe imaging optical system 12 according to the third example.

TABLE 4 f 4.565 mm F-NUMBER = 2.22 ω = 32.15° SURFACE Ri Di nd νd(APERTURE INFINITY 0.00000 STOP(s) 1 1.55020 1.04433 1.52528 55.98 27.22780 0.53487 3 −1.77007  0.39136 1.61422 25.58 4 −3.83009  0.37033 52.89854 1.30455 1.52528 65.95 6 3.70629 0.52540    7 (CG) INFINITY0.30000 1.51680 64.17 8 INFINITY 0.30000    9 (MLA) INFINITY 0.150001.45844 67.83 10  INFINITY 0.31088

The aspherical surface data of the imaging optical system 12 accordingto the third example is as follows.

First surface:

K=−0.20245

a4=0.003229775

a6=0.001694589

a8=0.02561581

a10=−0.08767680

a12=0.097495696

a14=−0.04023964

Second surface:

K=−6.895721

a4=−0.01976406

a6=−0.07477942

a8=0.104317366

a10=−0.23078865

a12=0.171090494

a14=−0.04583522

Third surface:

K=−1.09407719

a4=−0.1864082

a6=−0.2045030

a8=0.704900832

a10=−0.62715201

a12=−0.60554692

a14=1.57819371413

a16=−0.81214824

Fourth surface:

K=7.945479347

a4=−0.290128124

a6=0.266293358

a8=−0.05940777

a10=−0.00351743

a12=0.015588693

a14=0.034025947

a16=−0.01389210

Fifth surface:

K=−21.9355106

a4=−0.6349963

a6=0.793265391

a8=−1.4705880

a10=1.530192682

a12=0.140633914

a14=−1.07426579

a16=−0.7284073

a18=1.71623391

a20=−0.64358185

Sixth surface:

K=−23.3394184

a4=−0.12023343

a6=−0.02629781

a8=0.037999974

a10=−0.02143799

a12=−0.008517051

a14=−0.00388616

a16=0.001166162

a18=−0.00012250

a20=−0.00001139

f1/f=0.770

|f2|/f=1.254

f3/f=3.545

TL/f=1.121

D2/f=0.081

D5/f=0.286

hc(G2R)/(D1+D2+D3)=0.433

ν1−ν2=30.37

ρ=0.166

CRA (incident angle of chief ray onto image plane) (angle of view of 31degrees)=25.9°.

As described below, Condition Formulas (1) to (10) recited above aresatisfied in the example. As recited above, it can be seen that theimaging optical system 12 according to the third example has goodperformance.

Fourth Example

FIG. 35 illustrates the configuration of an imaging lens according to afourth example.

FIG. 36 and FIG. 37 are various aberration diagrams of the imaging lensaccording to the fourth example.

FIG. 38 illustrates the exit pupil position of the imaging lensaccording to the fourth example.

FIG. 39 illustrates the configurations and numerical values of the exitpupils of the imaging lens according to the fourth example.

Table 5 recited below shows the curvature radius Ri, the spacing Dic,the refractive index nd, and the dispersion value νd for the surfaces ofthe imaging optical system 12 according to the fourth example.

TABLE 5 f 4.365 mm F-NUMBER = 2.19 ω = 32.15° SURFACE Ri Di nd νd(APERTURE INFINITY 0.00000 STOP(s) 1 1.520799 0.72273 1.52528 55.95 25.224694 0.65994 3 −1.884574  0.39136 1.61422 25.58 4 −2.749460  0.545075 3.673851 1.30454 1.52528 55.95 6 3.272634 0.14555    7 (CG) INFINITY0.20000 1.51680 64.17 8 INFINITY 0.30000    9 (MLA) INFINITY 0.150001.45844 67.83 10  INFINITY 0.78034

The aspherical surface data of the imaging optical system 12 accordingto the fourth example is as follows.

First surface:

K=−0.14556925

a4=0.00865748

a6=0.01535309

a8=0.022838803

a10=−0.0807432

a12=0.101719532

a14=−0.04098285

Second surface:

K=−64.93822

a4=0.065296325

a6=−0.04793898

a8=0.072653147

a10=−0.13704764

a12=0.185529421

a14=−0.11017364

Third surface:

K=0.421682639

a4=−0.0838032

a6=−0.15298818

a8=0.671464289

a10=−0.7491886

a12=−0.3598329

a14=1.378890211

a16=−0.8109447

Fourth surface:

K=−9.97319261

a4=−0.23169433

a6=0.181826267

a8=−0.06421142

a10=0.018411689

a12=0.002007272

a14=0.007578708

a16=−0.00430411

Fifth surface:

K=−41.3232311

a4=−0.38012889

a6=0.473270827

a8=−1.27740830

a10=1.500018546

a12=0.119769405

a14=−1.18479210

a16=−0.66533645

a18=1.948821319

a20=−0.85388631

Sixth surface:

K=−9.37636765

a4=−0.17333756

a6=0.0800088524

a8=−0.06665131

a10=0.02565206

a12=0.006098033

a14=−0.00750137

a16=0.000734333

a18=0.000627152

a20=−0.00013698

f1/f=0.834

|f2|/f=2.560

f3/f=101.258

TL/f=1.139

D2/f=0.119

D5/f=0.286

hc(G2R)/(D1+D2+D3)=0.462

ν1−ν2=30.37

ρ=0.174

CRA (incident angle of chief ray onto image plane) (angle of view of 31degrees)=25.3°.

As described below, Condition Formulas (1) to (10) recited above aresatisfied in the example. As recited above, it can be seen that theimaging optical system 12 according to the fourth example has goodperformance.

Table 6 shows the values of the Condition Formulas of the examples.

TABLE 6 FIRST SECOND THIRD FOURTH EXAMPLE EXAMPLE EXAMPLE EXAMPLECONDITION 0.8 0.794 0.77 0.834 FORMULA (1) CONDITION 1.56 2.03 1.26 2.57FORMULA (2) CONDITION 5.31 103.68 3.55 103.93 FORMULA (3) CONDITION 1.121.095 1.12 1.12 FORMULA (4) CONDITION 0.093 0.104 0.081 0.119 FORMULA(5) CONDITION 0.276 0.281 0.285 0.284 FORMULA (6) CONDITION 0.42 0.4670.433 0.46 FORMULA (7) CONDITION 0.16 0.17 0.16 0.16 FORMULA (8)CONDITION 30.37 30.37 30.37 30.37 FORMULA (9) CONDITION 27.2° 26.1°25.8° 25.2° FORMULA (10)

As shown in Table 6, each of Condition Formulas (1) to (10) recitedabove is satisfied in the first to fourth examples.

According to the imaging lens and the solid state imaging deviceaccording to the embodiment as described above, both a high-precisionrange image and a good visible image can be acquired.

Although an embodiment and examples are described hereinabove, theinvention is not limited to these examples. For example, although theembodiment and examples recited above illustrate examples in which thecover glass (CG) and the microlens array (MLA) are provided, aconfiguration that includes only the microlens array (MLA) may be used.Also, the values illustrated in the examples recited above are merelyexamples; and other values may be used as long as the conditions of theinvention are satisfied. Further, additions, deletions, or designmodifications of the components or appropriate combinations of thefeatures of the embodiment appropriately made by one skilled in the artin regard to the embodiment and the examples described above are withinthe scope of the invention to the extent that the spirit of theinvention is included.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. An imaging lens, comprising: a first opticalsystem including an optical axis; and a microlens array provided betweenthe first optical system and an imaging element, the microlens arrayincluding a plurality of microlens units provided in a first plane, theimaging element including a plurality of pixel groups, each of the pixelgroups including a plurality of pixels, the microlens units respectivelyoverlapping the pixel groups when projected onto the first plane, thefirst optical system including: an aperture stop; a first lens providedbetween the aperture stop and the microlens array, the first lens havinga first surface, a second surface, and a positive refractive power, thefirst surface opposing the aperture stop, the second surface beingprovided between the first surface and the microlens array; a secondlens provided between the first lens and the microlens array, the secondlens having a third surface, a fourth surface, and a negative refractivepower, the third surface opposing the second surface, the fourth surfacebeing provided between the third surface and the microlens array; and athird lens provided between the second lens and the microlens array, thethird lens having a fifth surface, a sixth surface, and a positiverefractive power, the fifth surface opposing the fourth surface, thesixth surface being provided between the fifth surface and the microlensarray, a curvature radius of the first surface being positive, each of acurvature radius of the third surface and a curvature radius of thefourth surface being negative, each of a curvature radius of the fifthsurface and a curvature radius of the sixth surface being positive, atleast one selected from the first to sixth surfaces having an asphericalconfiguration, Formulas (1) to (6) being satisfied, where f is a focallength of the first optical system, f1 is a focal length of the firstlens, f2 is a focal length of the second lens, f3 is a focal length ofthe third lens, TL is a distance between the aperture stop and theimaging element, D2 is a distance along the optical axis between thesecond lens and the third lens, and D5 is a thickness along the opticalaxis of the third lens:0.6<f1/f<0.9  (1)1.0<|f2|/f<3.0  (2)2.0<f3/f<200  (3)f/TL<1.3  (4)0<D2/f<0.2  (5)0<D5/f<0.5  (6).
 2. The lens according to claim 1, wherein the microlensarray demagnifies an image formed by the first optical system, and ademagnification ratio of the image due to the microlens array is notless than 0.001 and not more than 0.87.
 3. The lens according to claim1, wherein Formula (7) is satisfied, where a distance between theoptical axis and a position where a chief ray of off-axis light raysintersects the fourth surface is hc(G2R), the off-axis light raysintersecting the optical axis, a distance along the optical axis betweenthe aperture stop and the fourth surface is D1+D2+D3, D1 is a thicknessalong the optical axis of the first lens, D2 is a product of a firstdistance and a first refractive index, the first distance being adistance along the optical axis between the first lens and the secondlens, the first refractive index being an index of a region between thefirst lens and the second lens, and D3 is a thickness along the opticalaxis of the second lens:0.3<hc(G2R)/(D1+D2+D3)<0.6  (7).
 4. The lens according to claim 1,wherein the first lens includes at least one selected from glass and aresin, and each of the second lens and the third lens includes a resin.5. The lens according to claim 1, wherein a configuration of off-axislight rays at an exit pupil plane of the first optical system has afirst diameter and a second diameter when the configuration is treatedas an ellipse, the off-axis light rays intersecting the optical axis,the first diameter being along a first direction in the exit pupilplane, the second diameter being along a second direction perpendicularto the first direction and in the exit pupil plane, Formula (8) issatisfied, where a is ½ times the first diameter, b is ½ times thesecond diameter, ρ is flattening, a=hx(EXTPURX),b=(hy(EXTPiUR)−hy(EXTPiDW))/2, and ρ=|1−b/a|, the off-axis light raysincludes: an upper light ray; a lower light ray positioned between theupper light ray and the optical axis at the exit pupil plane; and achief ray positioned between the upper light ray and the lower light rayat the exit pupil plane, hy(EXTPiUR) is a distance along the seconddirection between the optical axis and a position where the upper lightray passes through the exit pupil plane, hy(EXTPiDW) is a distance alongthe second direction between the optical axis and a position where thelower light ray passes through the exit pupil plane, and hx(EXTPURX) is½ times a length along the first direction of the off-axis light rays atthe exit pupil plane:0≦ρ<0.3  (8).
 6. The lens according to claim 1, wherein Formula (9) issatisfied, where ν1 is an Abbe number of the first lens, and ν2 is anAbbe number of the second lens:0≦ν1−ν2  (9).
 7. The lens according to claim 1, wherein Formula (10) issatisfied, where αi is an incident angle of a chief ray on a surfacewhere the pixels are provided, and the chief ray is a chief ray ofoff-axis light rays at a maximum angle of view, the off-axis light raystraveling in a direction intersecting the optical axis:20°≦αi≦30°  (10).
 8. The lens according to claim 1, further comprisingan optical filter provided between the first optical system and themicrolens array.
 9. The lens according to claim 1, wherein the imagingelement is provided between the first optical system and a virtualimaging point of the first optical system.
 10. A solid state imagingdevice, comprising: the imaging lens according to claim 1; and asolid-state imaging element to convert light passing through the imaginglens into an electrical signal.
 11. The device according to claim 10,wherein the solid-state imaging element outputs a plenoptic image. 12.The device according to claim 11, wherein the plenoptic image includes aplurality of picture cells, each of the picture cells corresponds to oneselected from a plurality of colors, the colors being different fromeach other, and the device adjusts a signal balance between the colorsof the plenoptic image.
 13. The device according to claim 11, whereinthe plenoptic image includes a plurality of picture cells including afirst picture cell corresponding to a signal of a first color, and thedevice estimates a signal of a second color of the first picture cell byreferring to a picture cell disposed around the first picture cell, thesecond color being different from the first color.
 14. The deviceaccording to claim 11, wherein the plenoptic image includes a pluralityof image points corresponding a first point on a subject, and the devicecalculates a correspondence between the first point and each of theimage points.
 15. The device according to claim 14, wherein the devicecalculates a two-dimensional image by synthesizing a picture cell valueof each of the image points based on the correspondence and calculatinga post-synthesis signal corresponding to the first point.